In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, or other workpieces with impurities. Ion implanters or ion implantation systems treat a workpiece with an ion beam, to produce n or p-type doped regions or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material, wherein implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n-type extrinsic material wafers, and implanting materials such as boron, gallium or indium creates p-type extrinsic material portions in a semiconductor wafer.
Ion beams employed in ion implantation systems typically have a smaller cross-sectional area than a substrate or wafer to be implanted. In order for the ion beam to completely cover the wafer, the ion beam and/or the wafer are moved relative to one another in order to scan the entire wafer surface. In one example, an ion beam is deflected so as to scan across a wafer, which is held in place. In another example, an ion beam remains fixed while a wafer is mechanically moved to allow the ion beam to scan across the wafer. In yet another example, the ion beam is scanned in a fast/horizontal direction while the wafer is mechanically moved in a slow/vertical direction.
Serial ion implantations generally operate on a single wafer at a time. Relative motion between an ion beam and wafer is effected so that the ion beam traces a raster pattern on the wafer surface. Typically, there is an amount of overlap between adjacent scan lines to facilitate uniform implantation.
However, instabilities in ion beams themselves can lead to non-uniform implantations. The instabilities can result from a number of sources, such as contamination on interior surfaces causing unwanted discharges in an ion source, and the like. As a result of the instabilities, a glitch can occur wherein a flux of the ion beam drops within a short period of time. The drop or change in flux leads to areas of the wafer receiving a lower level of doping, which can result in degraded or faulty devices. Additionally, an increase in flux can lead to areas of a wafer surface receiving a higher level of doping, which can also result in degraded or faulty devices.
For beam deflection based scanning systems or fixed beam systems with scanning wafer(s), multiple passes are generally made over each region of the wafer in order to obtain a sufficient dosing. An error in even a single pass results in an unwanted dose variation for the affected region.
A conventional mechanism exists for switching off an arc discharge source on detected ion beam instabilities. However, the mechanism is limited to arc discharge sources and requires a specific circuit limited to arc discharge sources.